Suspension systems for vehicles are well known in the art. Suspension systems have as their goal the control of relative motion between a sprung mass and an unsprung mass of a vehicle. One example of a system is a chassis suspension system of a vehicle, wherein the sprung mass includes the chassis and the unsprung mass includes the vehicle's suspension arms, wheels, tires, etc. Another example of a suspension system is a cab suspension system for a semi-truck tractor, wherein the sprung mass includes the tractor cab and the unsprung mass includes the tractor chassis.
Active suspension systems have at least one variable force actuator between the sprung and unsprung masses, and a controller for controlling the force actuator so as to control the system's inertia damping gain. The controller monitors various vehicle conditions to determine actuator control. In particular, the controller requires an inertially referenced velocity measurement of the sprung mass.
In practical experience, one economical manner to acquire an inertially referenced velocity measurement is to integrate a signal from an accelerometer transducer mounted on the sprung mass. Specifically, one common way to implement the integration process is to use a bandpass filter for filtering the signal from the accelerometer. The bandpass filter behaves as a pseudo-integrator within a range of frequencies at and around the resonant frequency of the sprung mass. Thus, the bandpass filter provides a velocity indicative signal to the controller. However, the bandpass filter method has performance limitations. For example, given sufficient force actuator dynamics, the bandpass filter may limit the achievable inertia damping gain.